The present invention relates to an electronic proximity switch and, more particularly, to an electronic proximity switch operating in a non-contact mode in a welding zone of welding facilities, with the proximity switch being adapted to, for example, control welding equipment such as welding tongs and/or check position of welding electrodes.
In welding facilities, especially in welding facilities employing butt welding machines, there is a considerable amount of floating welding globules and sparking or arcing. Conventional proximity switches generally have a housing of brass, steel or a ceramic material so as to readily withstand a corrosive action exerted by the welding environment; however, in all conventional housing materials used for proximity switches, an extensive slag formation is encountered at the proximity switch housing due to the floating welding globules within a relatively short period of time, whereby the switching characteristics and, especially, the response sensitivity of the proximity switch are noticeably impaired.
It has been proposed to utilize, for example, polytetrafluoroethylene caps to counteract the above noted problems; however, the utilization of such caps is disadvantageous in much as the caps themselves reduce an effective spacing especially in front of a response surface of the proximity switch by virtue of the fact that the caps are formed as threaded-on elements.
A further disadvantage of the utilization of caps resides in the fact that, by virtue of the nature of the material, namely, polytetrafluorethylene, it is extremely difficult to secure the caps in place and prevent any detachment of the caps so that any disturbances due to collision with the operating elements of the welding machine can easily arise. Furthermore, with the use of the caps of the aforementioned type, as can readily be appreciated, if the caps become detached, considerable problems arise in carrying out a welding operation.
The aim underlying the present invention essentially resides in providing a proximity switch which includes a housing constructed in such a manner that any slag layer formation along the housing is minimized if not avoided.
In accordance with advantageous features of the present invention, a proximity switch is provided having a housing wherein at least a portion of the housing generally exposed to sparks, arcing, or floating welding globules is provided with an anti-stick coating material of, for example, polytetrafluoroethylene or PFA (with perfluoroalkoxy side chains).
Experimentation by way of voluminous tests has revealed that by virtue of the utilization of such coating, the housings of the proximity switch do not experience any formation of a slag layer or, at most, only a slight adherence of a slag particle with can readily blasted off by means of a jet of compressed air or, the adhesions which may appear surprisingly disappear during a cleaning of the welding electrodes by means of a jet of compressed air.
Advantageously, in accordance with further features of the present invention, the housing of the proximity switch is provided, on a response-sensitive end face thereof, with a ceramic disk provided with an anti-adhesive coating with a shell of the housing consisting of, for example, bare brass having an anti-adhesive coating over at least a region thereof adjoining the response-sensitive end face.
According to the present invention, the ceramic disk is utilized to replace the synthetic resin cap which is usually required in proximity switches, as a thermal protection during application of the anti-stick coating.